A polarized light and scanning electron microscopic study of human fissureand lingual enamel of unerupted mandibular third molars

Using histological and ultrastructural techniques the aims of this study we re to investigate whether the mineralization pattern and surface microanato my of the caries-susceptible fissure enamel were different from those on th e caries-inactive lingual surface. The material consisted of 31 unerupted t hird mandibular molars. The specimens were initially grouped into four cate gories: (1) without, (2) with initial, (3) with almost completed and (4) wi th completed root formation. One ground section with fissure-like morpholog y was selected from each tooth. Using water as a medium the observed birefr ingence was negative along the lingual and fissure transverses in specimens with almost completed and with completed root formation, while the observe d birefringence was positive at different distances in the enamel in sectio ns representing less maturation stages. Qualitative imbibition studies reve aled hypomineralized enamel in the lower part of the fissures in specimens representing almost and completed root formation. Imbibed in quinoline, par ts of the hypomineralized enamel behaved like a molecular sieve due to the presence of micropores, indicating that the structural arrangement is diffe rent from that in the enamel adjacent to this areas. After division of the sections into a lingual and a buccal part, SEM features were described from lower and upper parts of the bucca I fissure wall and on lingual enamel in the area corresponding to the bottom part of the fissure. The surface micr oanatomy varied greatly. Negative developmental irregularities such as fiss ures and holes were associated with the immature enamel, while matured enam el - particularly fissures - housed many positive developmental irregularit ies such as enamel caps and protrusions. The crystal size in the mature spe cimens appeared smaller and more uniform than the crystals from the immatur e specimens. Apart from the occurrence of hypomineralized enamel in fissure s and numerous positive developmental irregularities on the fissure surface , no major differences between fissure and lingual enamel were noticed, nei ther with respect to mineralization pattern during final stages of tooth de velopment nor to the degree of surface porosity prior to tooth emergence.